There have been known image forming apparatuses including developing cartridges. One of such image forming apparatuses is configured to identify the specification of the developing cartridge or determine whether or not the developing cartridge is attached. For example, a prior art discloses a developing cartridge including a detection gear and protrusions moving together with rotation of the detection gear. In this configuration, an image forming apparatus senses the protrusions by means of a sensor to detect whether the developing cartridge is attached.